Preparation of oxygenated naphthenes



Patented Aug. 15, 1950 PREPARATION OF OXYGENATED N APHTHENES William I. Denton, Woodbury, N. J., assignor to Socony-Vacuum Oil Company, Incorporated, a

corporation of New York No Drawing. Application June 29, 1948, Serial No. 35,989

6 Claims. (01. 260-451) This invention has to do with the preparation of oxygenated naphthenes. More specifically, the present invention has to do with the preparation of naphthenic acids, alcohols, aldehydes, esters and ketones from selected alkyl-substituted, completely saturated naphthenes.

N aphthenes are well known in the art as cycloaliphatic hydrocarbons, as opposed to aliphatic and aromatic hydrocarbons. Completely saturated naphthenes are typified by cyclopentane, cyclohexane and tetralin, whereas unsaturated naphthenes are typified by cyclopentenes, cyclo hexenes and 2,3-dihydronaphthalene. It is with the alkyl-substituted, completely saturated naphthenes that this invention is concerned. Oxygenated naphthenes are illustrated by cyclopentane carboxylic acid, cyclophentyl acetic acid, cyclohexane carboxylic acid, cyclohexanol, etc.

As is well known to those familiar with the art, considerable attention has been directed to sources of naphthenic acids. Generally, such acids have been obtained by extraction of naphthenic type crude oils with various selective solvents, such as furfural, nitrobenzene, liquid sulfur dioxide and the like. While solvent extraction methods are useful, they are restricted to use with only a limited number of crude oils. Only a small number of crudes have sufliciently high concentrations of naphthenic acids to warrant solvent extraction in commercial practice. In addition, it is recognized that extraction procedures involve treatment of large quantities of crudes, necessitating sizable equipment for extraction and for recovery of selective solvent. Purification of the acids so extracted also presents a problem, for the acids generally have an unpleasant odor.

The limitations associated with solvent extraction procedures have led to investigation of other methods for obtaining naphthenic acids. One such method is oxidation of naphthenic type oils, such as Coastal gas oils. Oxidation of such oils, however, has not yet been commercially practical inasmuch as the oxygenated products thereof are mixtures of paraflinic, naphthenic and aromatic compounds, stemming from the paraflins, naphthenes and aromatics in the gas oils. With such a complex mixture, considerable difliculty has been encountered in separating the oxygenated naphthenes from the corresponding paraffinic and aromatic compounds, as well as from any unreacted hydrocarbons. Another shortcoming of previous oxidation procedures has appeared in excessive formation of carbon and oxides of carbon. Additionally, the oxygen-containing naphthe potential oxygen-containing naphthenes byv virtue of the naphthene ring or rings rupturing during the oxidation. Also, intercondensation of oxygenated products takes place, giving rise to tar-like materials. The oxidation conditions,

therefore, may be called destructive, in view of completely saturated naphthenes, having at leastabout per cent of the fraction boiling within.

a range of 75 F. and having an initial boiling point of at least about 250 F. In this oxidation procedure, none of the naphthenes present in the hydrocarbon fraction undergoes ring rupture and only small amounts are decomposed to carbon and carbon oxides. Together with the naphthenic acids formed in the present process are one or more of the following oxygenated naphthenes: alcohols, aldehydes, esters and ketones.

As indicated above, the hydrocarbon fraction used herein is one containing at least '75 per cent of alkyl-substituted, completely saturated naphthenes, having at least about 75 per cent of the fraction boiling within a range of 75 F., and having an initial boiling point of at least about 250 F. With such naphthenic fractions, formation of oxygen derivatives of paraffins and/or aromatics, in the oxidation operation, is substantially reduced, such that separation of the desired naphthenic acids and other oxygenated naphthenes is readily achieved. In addition, with the narrow boiling range of the naphthenic fraction, the hydrocarbons therein are of approximately the same molecular weight and have substantially the a same oxidation susceptibility. Hydrocarbon fractions which have proven particularly satisfactory are those having the aforesaid characteristics and having, however, at least per cent of the aforesaid naphthenes.

Typical naphthene fractions include selected cuts from highly naphthenic crudes and fractions consisting predominantly of completely hydrogenated alkyl aromatic hydrocarbons or alkyl naphthalenes. A preferred naphthene fraction is one having a boiling range of 420 F. to 535 F., with 75 per cent boiling between 435 F. and 510 thenic products are generally only a fraction of 55 F., and consisting predominantly, per cent, of

completely hydrogenated dimethyl and trimethyl naphthalenes. Another preferred fraction is one having a boiling range of 335 F. to 450 F., '75 per cent boiling from 368 F. to 440 F., and containing 80 per cent of completely saturated alkyl aromatics and monomethyl and dimethyl naphthalenes.

The naphthene fractions described above may be obtained by completely hydrogenating highly aromatic fractions. The hydrogenated product may then be separated into various distillate fractions to be used as charge materials for oxidation. Alternatively, the highly aromatic fractions may be distilled to relatively narrow boiling distillate fractions, and the latter, individually or collectively, may be completely hydrogenated. Conditions for completely hydrogenating aromatic hydrocarbons are well known in the art. Illustrative of such conditions are those used in forming the naphthene charge materials used herein. The naphthene charges were obtained by hydrogenating the aromatic fractions at about 550 F., with about 1500 pounds per square inch pressure, in the presence of a nickel catalyst.

Hydrogenation conditions are well known in the art, typical of which are provided in Reactions of Pure Hydrocarbons, Egloff, and The Chemistry of Petroleum Derivatives, volumes I and II, Ellis.

Limited oxidation conditions are used in the oxidation procedure whereby naphthenic acids and other oxygenated naphthenic compounds are formed. As indicated above, the naphthene (or cycloaliphatic) ring structure of the hydrocarbon reactant is preserved, with essentially no rupture of the ring. Under such conditions, there is substantially no carbon or carbon oxides in the product. Particularly satisfactory non-destructive or limited oxidation conditions are the following: vapor phase, non-catalytic operation with limited oxygen concentration. Temperatures used for vapor phase reaction are carefully controlled within the range of 250 F. to 600 F., with excellent results being obtained within the range of 325 F. to 500 F. With such temperatures, the pressure used may vary from 200 to 2000 pounds per square inch. Contact times used fall within the range of 0.1 to 60 minutes. Preferred pressure and contact time conditions are 300 to 750 pounds per square inch and 1 to 30 minutes. The oxygen to hydrocarbon molar proportion ratio should not exceed about 3-4 to 1; that is, depending upon the conditions used, 3 to 4 molar proportions of oxygen to 1 of hydrocarbon represent maximum oxygen concentration. For example, when a 3:1 molar ratio is used, it is desirable to use lower temperatures and shorter contact times and, conversely, with less than a 1:1 molar ratio higher temperatures may be used. While pressure has been used to speed up the reaction, similar results can be obtained by bubbling air through similar hydrocarbon stocks at elevated temperatures for protracted period (-50 hours), either with or without dissolved oxidation catalysts such as copper naphthenate, manganese oleate, etc.

Preferably, the oxygen concentration is maintained between 0.5 and 2.0 molar proportions of oxygen per molar proportion of hydrocarbon charge.

The following typical, and non-limiting, examples serve to further describe the invention.

Example I A highly aromatic fraction, with a boiling range of 400 F. to 600 F., was completely hydrogenated. The hydrogenation was carried out in the presence of a nickel catalyst, at a temperature of 500 F., and with a pressure of 1500 pounds per square inch. The hydrogenated product was then separated by distillation into several distillate fractions. The fraction used in the oxidation procedure had a boiling range of 420 F. to 535 F. and contained approximately per cent of completely hydrogenated dimethyl and trimethyl naphthalenes.

The naphthene charge was oxidized at a temperature of 490 F., with a pressure of 500 pounds per square inch and a contact time of 2.2 minutes. The molar ratio of air to hydrocarbon was 10:15, assigning an average molecular weight of 210 to the naphthene charge. The reactor used was a stainless steel pipe having an inside diameter of ,4; inch. The naphthene charge and oxygen were mixed and then treated in the reactor under the foregoing conditions. The oxidation product was collected and cooled. Equipment for this procedure is similar to that used in hydrocarbon oxidation operations and is familiar to those acquainted with the art.

The oxidation product was analyzed and found to have the following properties: a neutralization number (N. N.) of 17 mgms. KOH per gram of product, indicating '7 per cent of naphthenic acids; a hydroxyl number of 28 mgms. KOH per gram of product, indicating 11 per cent of naphthenic alcohols; a carbonyl number of 57 mgms. KOH per gram of product, indicating 22' per cent of naphthenic aldehydes and naphthenic ketones; and an average molecular weight of 220. The yield of naphthenic acids, alcohols, aldehydes and ketones is 40 per cent.

The acids were separated by extraction with caustic, after which the alcohols were recovered by formation of the boric acid ester. The aldehydes and ketones were recovered by solvent extraction. The naphthenic acids separated from the oxidation product are characterized by a pleasant odor, in contrast to the naphthenic acids separated from naphthenic crude oils.

Example II A naphthene fraction having a boiling range of 335 F. to 450 F., and containing 80 per cent of completely hydrogenated alkyl aromatics, and monomethyl and dimethyl naphthalenes, was oxidized under the following conditions: temperature, 550 F.; pressure, 500 pounds per square inch; contact time, 5 minutes; molar ratio of hydrocarbon to air, 1:9; reactor, 0.18 inch, inside diameter, nickel tube 15 feet in length. The naphthene fraction was prepared by completely hydrogenating a highly aromatic material having a boiling range of 380 F. to 475 F. The hydrogenation conditions were: 500 F.; 1500 pounds per square inch; and 20 per cent, by weight, of nickel catalyst.

The oxidation product obtained contained 2 per cent of naphthenic acids (N. N., 8 mgms. KOH/gram of product); 11 per cent of naphthenic alcohols (hydroxyl number, 35 mgms. KOH/gram of product); and 46 per cent of naphthenic aldehydes and naphthenic ketones (carbonyl number, mgms. KOH/gram of product). The yield of naphthenic acids, alcohols, aldehydes and ketones was 59 per cent.

The naphthenic alcohols, aldehydes and ketones may be oxidized to naphthenic acids by further oxidation, under the conditions shown above. Also, if naphthenic alcohols are desired.

the acids, aldehydes and ketones may be bydrogenated to the alcohols.

In sharp contrast to the foregoing illustrative examples is the following example which typifies prior oxidation procedures with naphthenic type oils.

Example III A Coastal gas oil having a boiling range of 400 F. to 750 F. and a naphthene content of approximately 50 per cent, was oxidized under the following conditions: temperature, 400' F.; pressure, 1000 pounds per square inch; contact time, approximately 3 minutes; molar ratio 'of hydrocarbon to air, 1:3 (oil rate, 6.6 gallons per hour; air rate, 245 cubic feet per hour) reactor, stainless steel tube inside diameter 0.54 inch.

During the oxidation, large amounts of oxides of carbon were formed. Deposition of carbon within the reactor tube was so great that plugs of carbon stopped the run even though a low temperature was used and the amount of oxygen was limited in an attempt to control the reaction.

The oxidation product obtained contained 4 per cent of mixed acidsnaphthenic, aromatic, and paraflinic ((N. N.) 9 mgm's. KOH/gram of product) 14 per cent of alcohols, also of a mixed character (hydroxyl number, 36 mgms. KOHj/ gram of product); 46 per cent of aldehydes and ketones, again of a mixed character (carbonyl number, 112 mgms. KOH/gram pf product). This represents a yield of 68 per cent of acids, alcohols, aldehydes and ketones of an aromatic and paraffinic character in addition to naphthenic. The complex nature of the oxidation product and the charge made separation of the various constituents a diflicult and tedious operation. In fact, the alcohols and ketones which represented the major oxygenated product were virtually impossible to recover in a pure state.

It is to be understood that the foregoing descriptive material and examples, particularly Examples I and II, serve to illustrate the invention and that the invention is not to be limited thereto; rather, the invention is to be construed in the light of the language of the appended claims. T;

I claim: j

1. The process for preparing oxygenated naphthenes, which comprises: oxidizing a naphtheiiic hydrocarbon fraction containing at least 75 per cent of alkyl-substituted, completely saturated naphthenes having at least 75 per cent boili'g within a range of 75 F. and having an init al boiling point of 250 F., in the vapor phase with oxygen, in the absence of a catalyst, at a ten??- perature between about 250 F. and 600 F., from about 0.1 to about 4.0 molar proportion of oxy en being used per molar proportion of said hydra;- carbon fraction.

2. The process for preparing oxygenated naphthenes, which comprises: oxidizing a naphthenic hydrocarbon fraction containing at least 85 per 6 cent of alkyl-substituted, completely saturated naphthenes having at least 75 per cent boiling within a range of 50 F. and having an initial boiling point of 250 F., in the vapor phase with oxygen, in the absence of a catalyst, at a temperature between about 325 F. and about 500 F" from about 0.5 to about 2.0 molar proportio'nof oxygen being used per molar proportion of said hydrocarbon fraction. Y

3. The process for preparing naphthenic acids, which comprises: oxidizing a naphthenic hydrocarbon fraction containing at least per cent of alkyl-substituted, completely saturated naph thenes having at least 75 per cent boiling within a range of 75 F. and having an initial boiling point of 250 F., in the vapor phase with oxygen, in the absence of a catalyst, at a temperature between about 250 F. and 600 F., from about 0.1 to about 4.0 molar proportion of oxygen being used per molar proportion of said hydrocarbon fraction; and separating naphthenic acids from the oxidation product thus formed.

4. The process for preparing naphthenic acids, which comprises: oxidizing a naphthenic hydro carbon fraction containing at least 85 per cent of alkyl-substituted, completely saturated naphthenes having at least 75 per cent boiling within a range of 50 F. and having an initial boiling point of 250 F., in the vapor phase with oxygen, in the absence of a catalyst, at a temperature between about 325 F. and 500 F., from about 0.5 to about 2.0 molar proportion of oxygen being used per molar proportion of said hydrocarbon fractions; and separating naphthenic acids from oxidation product thus formed.

5. The process for preparing naphthenic acids, which comprises: oxidizing a naphthenic hydrocarbon fraction containing about per cent of completely saturated, monomethyl and dimethyl naphthalenes having a boiling range from about 335 F. to about 450 F., in the vapor phase with air, in the absence of a catalyst, at a temperature of about 550 F., the molar ratio of hydrocarbon to air being about 1:9; and separating naphthenic acids from the oxidation product thus formed.

6. The process for preparing oxygenated naphthenes comprising acids, alcohols, aldehydes and ketones, which comprises: oxidizing a hydrocarbon charge consisting essentially of a naphthenic hydrocarbon fraction containing about 90. per cent of completely saturated, dimethyl and tri-, methyl napthalenes having a boiling range from about 420" F. to about 535 F. in the vapor phase with airat a temperature of about 490 F., the molar ratio of hydrocarbon to air being about 1.5:10, and separating said oxygenated naphthenes from the oxidation product thus formed.

WILLIAM I. DENTON.

REFERENCES CITED Forrest et al July 4, 1938 Mattox May 5, 1942 Number 

1. THE PROCESS FOR PREPARING OXYGENATED NAPHTHENES, WHICH COMPRISES: OXIDIZING A NAPHTENIC HYDROCARBON FRACTION CONTAINING AT LEAST 75 PER CENT OF ALKYL-SUBSTITUTED, COMPLETELY SATURATED NAPHTHENES HAVING AT LEAST 75 PER CENT BOILING WITHIN A RANGE OF 75*F. AND HAVING AN INITIAL BOILING POINT OF 250*F., IN THE VAPOR PHASE WITH OXYGEN, IN THE ABSENCE OF A CATALYST, AT A TEMPERATURE BETWEEN ABOUT 250*F. AND 600*F., FROM ABOUT 0.1 TO ABOUT 4.0 MOLAR PROPORTION OF OXYGEN BEING USED PER MOLAR PROPORTION OF SAID HYDROCARBON FRACTION. 